The color depth recording is a technology for recording, on a recording medium, data representing the color depth of the original image, with the gradation of each color in the RGB or YCrCb color space being assigned a predetermined bit length. In images recorded on an existing recording medium for playback or display, the luminance Y, red color difference Cr and blue color difference Cb are each represented by an eight-bit pixel bit value, namely an eight-bit gradation bit sequence.